The instant invention relates to the method of making amino acid acrylic monomers, particularly for use in compositions suitable for dental repair; i.e., a dental filling for dental adhesive.
There have been repeated efforts to replace amalgam as a filling in dental practice, as well as to have suitable adhesives for dental purposes other than for fillings. One polymeric material that has been suggested for such use is bis-glycidylmethylmethacrylate polymer (bis-GMA). When used as a dental adhesive or filling, together with the other usual components admixed therewith, such bis-GMA offers good mechanical and physical properties, but exhibits considerable post-shrinkage and relative poor adhesion to bone substrate. Thus, it is not entirely satisfactory for use as an adhesive in dental work or as a filling. The use of such GMA material is disclosed in U.S. Pat. Nos. 4,588,756 and 4,964,911.
U.S. Pat. No. 4,659,751 discusses the use of a variety of acids and other materials in order to treat the surface of teeth, such as enamel and dentin, to activate the surfaces for improved adhesion to polymers, but no disclosure or suggestion is made therein of the use of the GMA or bis-GMA.
In this regard, it is well known that in order to achieve desired bonding on enamel or dentin, the protein coatings on the enamel and the smear level on dentin must be removed. Traditionally, this has been done utilizing organic acids such as phosphoric, citric, and lactic acids, as well as ethylene diamine dicarboxylic acid. Accordingly, many of the new products provide such polyacids as surface cleaning and priming agents for enamel and dentin. At the present time bis-GMA resins themselves are not inherently adhesive to tooth surfaces, and if used acid etching is required.
Dibasic amino acids partially esterified with allyl alcohol or a hydroxyalkyl acrylate or methacrylate and cyclized have been found to overcome the problems associated with bis-GMA and such are disclosed in detail in the parent application identified above whose entire disclosure is specifically incorporated herein by reference.
However, it has been found that the method of making such partially esterified materials is material intensive, time consuming, and most importantly require such high acid strength that it often resulted in complete esterification leaving little or no functionality for adhesion to dentin. Moreover, the amino group remaining in the structure were so sterically hindered by the large acrylate or methacrylate moiety at each end, that it was difficult to formulate the esters as adhesive primers for dental use.